Method and apparatus for initiating communications on a shared channel in a mobile communication system

ABSTRACT

A method and apparatus for initiating communications on a shared channel in a mobile communication system are provided. A user equipment transmits an uplink signal for requesting communications on the shared channel to a Node B, and waits for a delay duration without monitoring a downlink after transmitting the uplink signal. When the delay duration has elapsed, the user equipment monitors the downlink during a valid period and determines whether a downlink signal responding to the uplink signal is received in a transmission time interval within the valid period. When the downlink signal is received in the valid period, the user equipment transmits and receives data on the shared channel.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 14/866,170, filed on Sep. 25, 2015, which issued as U.S. Pat. No.10,237,895 on Mar. 19, 2019; which is a continuation application ofprior U.S. patent application Ser. No. 14/176,738, filed Feb. 10, 2014,which has issued as U.S. Pat. No. 9,288,825 on Mar. 15, 2016; which is acontinuation of U.S. patent application Ser. No. 11/603,237, filed onNov. 22, 2006, which issued as U.S. Pat. No. 8,670,392 on Mar. 11, 2014;and which claims the benefit under 35 U.S.C. § 119(a) of Korean PatentApplication filed in the Korean Intellectual Property Office on Nov. 24,2005 and assigned Serial No. 10-2005-0113193, the entire disclosure ofeach of which is hereby incorporated by reference.

BACKGROUND 1. Field

The present invention generally relates to a mobile communicationsystem. More particularly, the present invention relates to a method andapparatus for initiating communications on a shared channel.

2. Description of the Related Art

A Universal Mobile Telecommunication Service (UNITS) system is athird-generation asynchronous mobile communication system using WidebandCode Division Multiple Access (WCDMA) based on General Packet RadioServices (GPRS) and a Global System for Mobile Communications (GSM)serving as a European mobile communication system.

In the Third-Generation Partnership Project (3GPP) responsible for UMTSstandardization, Long Term Evolution (LTE) of the UMTS system is underdiscussion. The LTE is targeted for commercialization around 2010 and isa technology for implementing high-speed packet based communication atabout 100 Mbps. For this, many methods are being considered. Forexample, there are methods for reducing the number of nodes on acommunication path by simplifying a network structure, for enablingwireless protocols in close proximity to a radio channel, and the like.It is predicted that an LTE structure will be changed from a 4-nodestructure of the legacy UMTS system to a 2- or 3-node structure.

FIG. 1 illustrates an example of a structure of an evolved UMTS mobilecommunication system. As illustrated in FIG. 1, Evolved Radio AccessNetworks (E-RANs) 110 and 112 are simplified into 2-node structures ofEvolved Node Bs (ENBs) 120, 122, 124, 126, and 128 and Evolved GatewayGPRS Serving Nodes (EGGSNs) 130 and 132. A User Equipment (UE) 101connects to an Internet Protocol (IP) network 114 over the E-RANs 110and 112.

The ENBs 120 to 128 are based on legacy Node Bs of the UMTS system andconnect to the UE 101 through a radio channel. In comparison with thelegacy Node Bs, the ENBs 120 to 128 perform more complex functions.Because all user traffics as well as a real-time service of Voice overIP (VoIP) are transmitted on a Shared Channel (SCH) in the LTE system, adevice is required which can collect information of UEs and perform ascheduling process. The ENBs 120 to 128 are responsible for thescheduling process.

The term “evolved” is used to distinguish the 3GPP LTE system from thelegacy UMTS system. To avoid the confusion in the following description,the terms “UE”, “Node B” and “network” are simply used.

The LTE system performs a Hybrid Automatic Retransmission Request (HARQ)between a Node B and a UE as in High Speed Downlink Packet Access(HSDPA) and Enhanced uplink Dedicated Channel (E-DCH). The HARQ is ascheme for increasing a probability of successful reception by softcombining previously received data with retransmitted data withoutdiscarding previously received data. However, because various Quality ofService (QoS) requirements cannot be satisfied only by the HARQ scheme,an outer ARQ can be performed in a higher layer. The outer ARQ is alsoperformed between a Node B and a UE.

To implement a transmission rate of a maximum of 100 Mbps, the LTEsystem can employ a wireless access technology of Orthogonal FrequencyDivision Multiplexing (OFDM) at a bandwidth of 20 MHz. The UE can applyan Adaptive Modulation & Coding (AMC) scheme for setting a modulationscheme and a channel coding rate proper for a channel state.

In the LTE system constructed as described above, every data istransmitted and received on an SCH. A process for transmitting andreceiving data on the SCH will be described with reference to FIG. 2. InFIG. 2, a receiver 205 and a transmitter 210 include a UE and a Node Bin downlink, respectively, or a Node B and a UE in uplink, respectively.In the case of downlink communication as described below, the receiver205 is the UE and the transmitter 210 is the Node B.

Before a packet is transmitted on the SCH in FIG. 2, the Node B 210first transmits per packet control information on a Shared ControlChannel (SCCH) in step 215. The per packet control informationcorresponds to a short Identifier (ID) of the UE 205 for receiving apacket, a packet size, a radio channel on which the packet istransmitted, a modulation scheme, channel coding, a HARQ, and the like.When receiving the per packet control information, the UE 205 determineswhether its own short ID is equal to that included in the per packetcontrol information and determines whether to receive a subsequentpacket.

When the two short IDs are the same, the UE 205 receives a user datapacket on the SCH, decodes the packet on the basis of the per packetcontrol information, and performs an error check in step 220. The UE 205transmits an Acknowledge (ACK) or Non-acknowledge (NACK) message to theNode B 210 on the basis of an error check result in step 225.

It is preferred that a size of the short ID of the UE is minimizedbecause the short ID of the UE is information to be continuouslytransmitted on the SCCH (upon transmission of every packet). The shortID of the UE has a unique value within a cell. The Node B is responsiblefor allocating and de-allocating short IDs for UEs within a cell. Thus,when the UE is powered on or moves to a new cell, the UE desiring totransmit and receive data on the SCH should receive a new short IDallocated from a Node B of a current cell or the new cell.

A message for allocating the short ID cannot be transmitted on the SCHand therefore uses a new type of channel rather than the SCH indownlink. Next, an operation for receiving a newly allocated short IDwill be described when the UE is powered on or moves to a new cell.

FIG. 3 is a message flow diagram illustrating a conventional operationfor acquiring a short ID after a UE moves to a new cell.

Referring to FIG. 3, a UE 305 acquires system information from a Node B310 of a current cell or a new cell when it is powered on or moves tothe new cell in step 315. The system information is common informationto be provided up to a cell boundary through known cell-by-cellchannels, and includes information to be detected by the UE 305 forinitiating communications in the cell. For example, the systeminformation is random access information, neighbor cell information, andthe like.

In step 320, the UE 305 transmits an Initial Uplink Message (IUM) on aRandom Access Channel (RACH) using the acquired system information. Ingeneral, the IUM is used to notify a network of the presence of the UE305, and contains a unique ID, capability information, and the like.When receiving the IUM, the Node B 310 sets a short ID to be allocatedto the UE 305. In step 325, the short ID is contained in an InitialDownlink Message (IDM) and is transmitted to the UE 305. Before data istransmitted, the IDM is first transmitted from the Node B 310 to the UE305. In addition, information required to use the SCH in the UE 305 isbasically contained in the IDM. For example, the required information isabout a Channel Quality Information (CQI) transmission scheme,transmission channel or HARQ configuration. The IDM is transmitted on aForward Access Channel (FACH) rather than the SCH. The FACH serving as adownlink channel to be transmitted up to a cell boundary is not appliedto the HARQ or AMC, which is different from the SCH. In step 330, the UE305 receives the IDM, detects the short ID, and transmits and receivesdata on the SCH.

Accordingly, there is a need for an improved method and apparatus inwhich a UE initiates communications on a shared channel to initiate adata transmission and reception on the shared channel.

SUMMARY

An aspect of exemplary embodiments of the present invention is toaddress at least the above problems and/or disadvantages and to provideat least the advantages described below. Accordingly, an aspect ofexemplary embodiments of the present invention is to provide a methodand apparatus for initiating a data transmission and reception on ashared channel.

In accordance with an aspect of exemplary embodiments of the presentinvention, there is provided a method for initiating communications on ashared channel in a mobile communication system, in which an uplinksignal for requesting communications is transmitted on the sharedchannel to a Node B; a delay duration without monitoring a downlink isprovided after transmitting the uplink signal; the downlink is monitoredduring a valid period after the delay duration has elapsed and whether adownlink signal responding to the uplink signal is received in onetransmission time interval within the valid period is determined; anddata on the shared channel is transmitted and received when the downlinksignal is received in the valid period.

In accordance with another aspect of exemplary embodiments of thepresent invention, there is provided a user equipment for initiatingcommunications on a shared channel in a mobile communication system, inwhich an uplink signal generator generates an uplink signal forrequesting communications on the shared channel and transmits thegenerated uplink signal to a Node B. A downlink signal processor waitsfor a delay duration without monitoring a downlink after transmittingthe uplink signal, monitors the downlink during a valid period after thedelay duration has elapsed and determines whether a downlink signalresponding to the uplink signal is received in one transmission timeinterval within the valid period. A shared channel processor transmitsand receives data on the shared channel when the downlink signal isreceived in the valid period.

In accordance with yet another aspect of exemplary embodiments of thepresent invention, there is provided a method for initiatingcommunications on a shared channel in a mobile communication system, inwhich an uplink signal for requesting communications on the sharedchannel is received from a user equipment. After waiting for a delayduration after receiving the uplink signal, a downlink signal istransmitted in one transmission time interval within a valid period inresponse to the uplink signal. Data on the shared channel is transmittedand received after transmitting the downlink signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an example of a structure of an evolved mobilecommunication system;

FIG. 2 schematically illustrates a data transmission and reception on aShared Channel (SCH);

FIG. 3 is a message flow diagram illustrating a conventional operationfor acquiring a short Identifier (ID) after a User Equipment (UE) movesto a new cell;

FIG. 4 is a message flow diagram illustrating an operation for acquiringa short ID from a SCH after a UE moves to a new cell in accordance withan exemplary embodiment of the present invention;

FIG. 5 illustrates a situation in which a collision of temporary IDsoccurs;

FIG. 6 illustrates an operation for preventing the collision oftemporary IDs using a valid period;

FIG. 7 is a flowchart illustrating an operation of the UE in accordancewith an exemplary embodiment of the present invention;

FIG. 8 is a block diagram illustrating a structure of the UE inaccordance with an exemplary embodiment of the present invention;

FIG. 9 is a flowchart illustrating an operation for acquiring a short IDfrom a Shared Control Channel (SCCH) in accordance with an exemplaryembodiment of the present invention;

FIGS. 10A and 10B illustrate structures of a per packet controlinformation message and a dedicated short ID allocation message inaccordance with an exemplary embodiment of the present invention;

FIG. 11 is a flowchart illustrating an operation of the UE in accordancewith an exemplary embodiment of the present invention; and

FIG. 12 is a block diagram illustrating a structure of the UE inaccordance with an exemplary embodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures

DETAILED DESCRIPTION

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofexemplary embodiments of the invention. Accordingly, those of ordinaryskill in the art will recognize that various changes and modificationsof the embodiments described herein can be made without departing fromthe scope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

The subject matter of exemplary embodiments of the present invention isto transmit a data packet on a Shared Channel (SCH) in a mobilecommunication system. A User Equipment (UE) transmits a signal includinga message for requesting use of the SCH to a Node B. When a response tothe signal is received, the SCH operates. A process for establishing andemploying the SCH between the UE and the Node B is referred to as theSCH initiation.

Next, exemplary embodiments of the present invention will be describedwith reference to a Third-Generation Partnership Project (3GPP) LongTerm Evolution (LTE) system using Orthogonal Frequency DivisionMultiplexing (OFDM) based on a Universal Mobile TelecommunicationService (UMTS) system. Those skilled in the art will appreciate that theuse of the SCH can be modified in other mobile communication systemshaving a technical background and a channel form analogous to thosedescribed in the context of exemplary embodiments of the presentinvention without departing from the scope of the present invention.

FIG. 4 is a message flow diagram illustrating an operation for acquiringa short Identifier (ID) from a SCH after a UE moves to a new cell inaccordance with an exemplary embodiment of the present invention.Herein, a Node B 410 covers a cell A, and a UE 405 is powered on in thecell A or moves from a different cell to the cell A.

Referring to FIG. 4, the Node B 410 manages cell-by-cell temporary IDpools in step 415. The temporary ID pools may be some of all assignableshort IDs and may be the same or different between cells. When a size ofeach short ID is, for example, 10 bits, 1024 Short IDs 0˜1023 can beprovided. Some of these short IDs can be set to temporary IDs on acell-by-cell basis. However, the same short ID pool can be managed forall the cells. For example, a temporary ID pool of the cell A has ShortIDs 0˜23.

In step 420, the UE 405 acquires system information from a BroadcastingChannel (BCH) of the Node B 410. The system information includes thetemporary ID pool of the cell A. The UE 405 stores the temporary IDpool. In the above example, the UE 405 detects that the temporary IDpool of the cell A is constructed with twenty-four (24) short IDsincluding Short IDs zero (0) to twenty-three (23).

In step 425, the UE 405 randomly selects one of the short IDs belongingto the temporary ID pool before transmitting an Initial Uplink Message(IUM) on a Random Access Channel (RACH). In step 430, the UE 405transmits the IUM on the RACH. The IUM is used to request use of the SCHwhile notifying a network of the presence of the UE 405. The IUM caninclude a unique ID and capability information of the UE 405 and theselected temporary ID. In step 435, the UE 405 monitors a Downlink SCCH(DL SCCH) after transmitting the IUM and determines whether a messagemapped to the IUM, that is, a message having the selected temporary ID,is received.

In step 445, the Node B 410 sets a dedicated short ID to be allocated tothe UE 405 in response to the received IUM, includes the dedicated shortID in an Initial Downlink Message (IDM), and transmits the IDM with thededicated short ID to the UE 405 through the SCH. In addition,information required to use the SCH in the UE 405 is contained in theIDM. For example, the required information corresponds to a ChannelQuality Information (CQI) transmission scheme, a transmission channel,or Hybrid Automatic Retransmission Request (HARQ) configuration. Whenthe IDM is transmitted on the SCH, the Node B 410 transmits per packetcontrol information including the selected temporary ID on the SCCH suchthat the UE 405 can receive the IDM in step 440. Herein, the per packetcontrol information includes reception parameters required to demodulateand decode a downlink packet in the UE 405, for example, informationcorresponding to a UE ID, a packet size, a modulation scheme, a HARQ,and the like. In step 450, the UE 405 receives the IDM by referring tothe per packet control information, determines that the initiation fordata transmission and/or reception has been completed by detecting adedicated short ID contained in the IDM, and starts to transmit andreceive data on the SCH using the dedicated short ID.

In the exemplary embodiment of the present invention as described above,the temporary ID is used to receive the IDM for allocating the dedicatedshort ID on the SCH. However, when at least two UEs within one cellselect the same temporary ID, the Node B cannot identify the UEs usingtemporary IDs. This is referred to as a collision of temporary IDs.

FIG. 5 illustrates a situation in which the collision of temporary IDsoccurs. Referring to FIG. 5, a UE 1 selects a temporary ID x and sends afirst IUM at a time 505 and a UE 2 selects the same temporary ID x andsends a second IUM at a time 515. After sending the first RIM, the UE 1monitors a SCCH during a time 510. After sending the second IUM, the UE2 monitors the SCCH during a time 520.

In response to the first IUM sent from the UE 1, a Node B sets adedicated short ID y for the UE 1 and then sends the SCCH with thetemporary ID x at a time 525. Then, the Node B includes the dedicatedshort ID y in an IDM and sends the IDM with the dedicated short ID y tothe UE 1 at a time 530. At this time, both the UE 1 and UE 2 wait forthe temporary ID x to be sent on the SCCH and receive the IDMtransmitted on the SCH. Thus, the UE 2 may make a wrong determinationthat the dedicated short ID has been allocated to the UE 2.

This problem occurs when multiple UEs select the same temporary IDduring a relatively short time. To address the problem, a method forincreasing a size of a temporary ID pool or decreasing a time in whichan operation error occurs can be considered. However, the method forincreasing the size of the temporary ID pool is not preferred because ofa decrease in the number of dedicated short IDs. For this reason, the UEmonitors the SCCH during a predefined valid period P after waiting for apredefined delay duration T without starting to monitor the SCCHimmediately after a signal for requesting use of the SCH including atemporary ID is transmitted. A response signal transmitted by the Node Bthrough the SCCH can be received in a transmission time interval withinthe valid period P. Thus, the time in which an operation error may occuris limited to within the valid period in which the SCCH is monitored. Inan exemplary implementation, the valid period P is set which includesmultiple transmission time intervals rather than one specifictransmission time interval.

FIG. 6 illustrates an operation for preventing the collision oftemporary IDs in accordance with an exemplary embodiment of the presentinvention.

Referring to FIG. 6, a UE selects a temporary ID x, includes thetemporary ID x in an IUM, and provides a Node B with the IUM as a signalfor requesting use of an SCH at a time 605. After sending the IUM, theUE waits for a delay duration 610 of T without monitoring a SCCH. Afterthe delay duration 610 ends, the UE monitors a response signal sent fromthe Node B through the SCCH during a valid period 615 of P. When thetemporary ID x is detected in the valid period 615, the UE tries toreceive an IDM on the SCH. On the other hand, when the temporary ID x isnot detected in the P period 615, the UE determines that the SCHinitiation has failed.

The Node B sends the SCCH with a temporary ID at a time 620 of onetransmission time interval in a period of [T, T+P] after receiving theIUM. Then, the Node B sends an IDM with a dedicated short ID to the UE.

In an exemplary implementation, the delay duration T causing delay issmall. However, when the delay duration T is set to an excessively smallvalue, processing capability is degraded in the Node B. Thus, the Node Bcannot prepare per packet control information with a temporary ID beforethe valid period P is reached. Therefore, T and P closely related to theprocessing capability of the Node B can have different values on acell-by-cell basis. The T and P values are included in systeminformation to be transmitted on the cell-by-cell basis and are providedto UEs.

FIG. 7 is a flowchart illustrating an operation of the UE in accordancewith an exemplary embodiment of the present invention.

Referring to FIG. 7, the UE generates an IUM for initiatingcommunications on a SCH in a current cell in step 705 and acquires atemporary ID pool of the current cell and T and P values in step 710.The UE acquires the temporary ID pool and the T and P values from systeminformation broadcast from a Node B of the current cell. If the IUM isgenerated, it means that a short ID to be used in the current cell isnot acquired as the UE is powered on or newly moves to the current cell.If the temporary ID pool is acquired, it means that the UE detectstemporary IDs available in the current cell.

In step 715, the UE selects one temporary ID from the temporary ID pool.At this time, all temporary IDs can be selected in the same probability.In step 720, the UE sends the IUM with the selected temporary ID to theNode B. In step 725, the UE waits for the delay duration T withoutmonitoring a DL SCCH after sending the IUM. When the delay duration Thas elapsed, the UE monitors the SCCH during the valid period P in step730. The UE determines whether per packet control information with theselected temporary ID is received on the SCCH in step 735. If theselected temporary ID is detected from the SCCH in the valid period P,the UE proceeds to step 740. Otherwise, the UE proceeds to step 750.

In step 740, the UE receives an IDM on the SCH by referring to the perpacket control information. In step 745, the UE sets a short ID includedin the IDM to its own dedicated short ID and then transmits and receivesdata on the SCH using the short ID. On the other hand, the UE determinesthat the initiation for communications on the SCH has failed and thenperforms a required subsequent operation in step 750. For example, theUE retransmits the RIM.

FIG. 8 is a block diagram illustrating a structure of the UE inaccordance with an exemplary embodiment of the present invention. Asillustrated in FIG. 8, the UE is provided with a control messagegenerator 805, a control message processor 825, a controller 835, ashort ID manager 810, a SCCH processor 815, a SCH processor 820, and atransceiver 830.

Referring to FIG. 8, the controller 835 controls an operation of the UErelated to radio resources. For example, the controller 835 performs anoperation for establishing or releasing a radio channel or an operationfor setting information to be inserted into an uplink control message.The controller 835 delivers the information to be inserted into an IUMto the control message generator 805. The controller 835, for example,manages a temporary ID pool and T and P values acquired from systeminformation of a current cell, selects a temporary ID from the temporaryID pool, and delivers the selected temporary ID to the control messagegenerator 805.

The control message generator 805 generates the uplink control messageusing the information received from the controller 835. For example, thecontrol message generator 805 generates the IUM using information suchas the temporary ID and the like delivered from the controller 835 anddelivers the generated IUM to the transceiver 830. The transceiver 830transmits a message or data to and receives a message or data from a UEthrough a radio channel.

When the controller 835 is notified that the IUM has been transmittedfrom the control message generator 805, the controller 835 waits for thedelay duration T and delivers the selected temporary ID and the P valueto the short ID manager 810. The short ID manager 810 is responsible foractivating or deactivating a short ID, and activates a short ID receivedfrom the controller 835 during the valid period P in response to acommand of the controller 835. If the short ID is activated, it meansthat a control operation is performed such that the SCCH processor 815detects a message with the activated short ID from per packet controlinformation received on the SCCH. When the controller 835 provides thetemporary ID, the short ID manager 810 controls the SCCH processor 815to detect a message with the temporary ID.

When detecting per packet control information with a short ID activatedby the short ID manager 810, particularly the temporary ID, from theSCCH, the SCCH processor 815 delivers the per packet control informationto the SCH processor 820. When receiving the per packet controlinformation from the SCCH processor 815, the SCH processor 820 detects apacket from the SCH, processes (or demodulates/decodes) the detectedpacket using the per packet control information, and delivers asuccessfully processed packet to a suitable device. When the packet isan IDM transmitted on the SCH, the IDM is delivered to the controlmessage processor 825. Otherwise, the packet is delivered to anassociated application section.

The control message processor 825 delivers control information containedin the IDM to the controller 835. The controller 835 provides the shortID manager 810 with a dedicated short ID of the information deliveredfrom the control message processor 825. At this time, an activationperiod of the dedicated short ID is continuously maintained until aspecial command is issued. The short ID manager 810 controls the SCCHprocessor 815 to detect per packet control information with thededicated short ID during the activation period of the dedicated shortID. Thus, the dedicated short ID is applied for transmission andreception of data on the SCH.

In an exemplary embodiment of the present invention, a dedicated shortID is transmitted on the SCCH. FIG. 9 is a flowchart illustrating anoperation for acquiring a short ID from the SCCH in accordance with anexemplary embodiment of the present invention. Herein, a Node B 910covers a cell A and a UE 905 is powered on in the cell A or moves from adifferent cell to the cell A.

Referring to FIG. 9, the Node B 910 manages temporary ID pools on acell-by-cell basis in step 915. Because a temporary ID is distinguishedfrom a general short ID in an exemplary embodiment, the cell-by-celltemporary ID pools do not need to be differently applied. The sametemporary ID pool can be applied to all the cells.

In step 920, the UE 905 acquires system information from a BCH of theNode B 910. The system information includes a temporary ID pool of thecell A, a delay duration T, and a valid period P. In step 925, the UE905 randomly selects one of temporary IDs belonging to the temporary IDpool before transmitting an RIM on a RACH. In step 930, the UE 905 sendsthe IUM on the RACH. In general, the IUM is used to request use of theSCH while notifying a network of the presence of the UE 905. The IUM caninclude a unique ID and capability information of the UE 905 and theselected temporary ID. In step 935, the UE 905 monitors a DL SCCH aftersending the IUM and determines whether a message mapped to the IUM, thatis, a message with the selected temporary ID, is received.

In step 940, the Node B 910 sets a dedicated short ID to be allocated tothe UE 905 in response to the received IUM and sends a dedicated shortID allocation message with the dedicated short ID and the temporary IDcontained in the IUM using the SCCH. When detecting the temporary IDcontained in the dedicated short ID allocation message, the UE can usethe dedicated short ID contained in the dedicated short ID allocationmessage to transmit and receive data on the SCH.

In step 945, the Node B 910 transmits per packet control informationwith the dedicated short ID on the SCCH in a normal DL SCH transmissionprocess for sending an IDM. In step 950, the Node B 910 transmits theIDM on the SCH. In step 955, the UE 905 receives the IDM and transmitsand receives data on the SCH using the dedicated short ID.

As described above, different messages for transmitting the per packetcontrol information and allocating the dedicated short ID through theSCCH are provided. The different messages are distinguished by messagetypes. FIGS. 10A and 10B illustrate structures of a per packet controlinformation message and a dedicated short ID allocation message inaccordance with an exemplary embodiment of the present invention.

Referring to FIG. 10A, a per packet control information message 1005contains per packet control information about a packet to be transmittedon a SCH. The per packet control information includes, for example, aModulation Scheme (MS) field 1015 for indicating an MS applied to thepacket, a dedicate short ID 1020 for identifying a UE for receiving thepacket, a resource field 1025 for indicating a radio channel on whichthe packet is transmitted (that is, a timeslot of an allocatedsubcarrier), a size field 1030 for indicating a size of the packet, aHARQ ID 1035 for identifying a HARQ processor of the packet, aRetransmission Serial Number (RSN) 1040, a Cyclic Redundancy Check code(CRC) field 1045, and the like.

A first bit 1010 of the per packet control information message 1005 isallocated to distinguish the per packet control information message 1005from the dedicated short ID allocation message 1050. That is, if thefirst bit is 0, it means that the message is the per packet controlinformation message 1005.

The dedicated short ID allocation message 1050 is provided with adedicated short ID 1060, a temporary ID 1065, and a CRC field 1070. Adedicated short ID to be allocated to a UE is inserted into thededicated short ID field 1060. A temporary ID reported from the UE isinserted into the temporary ID field 1065. A CRC operation result for amessage transmitted on the SCCH is inserted into the CRC field 1070.

Because a modulation scheme for a packet does not need to be indicatedin the dedicated short ID allocation message 1050, first two bits 1055of the dedicated short ID allocation message 1050 are allocated todistinguish the dedicated short ID allocation message 1050 from the perpacket control information message 1005. That is, if the first two bits1055 are 10, it means that the message is the dedicated short IDallocation message 1050.

FIG. 11 is a flowchart illustrating an operation of the UE in accordancewith an exemplary embodiment of the present invention.

Referring to FIG. 11, the UE generates an IUM for initiatingcommunications on a SCH in a current cell in step 1105 and acquires atemporary ID pool of the current cell and T and P values in step 1110.The UE acquires the temporary ID pool and the T and P values from systeminformation broadcast from a Node B of the current cell. If the IUM isgenerated, it means that a short ID to be used in the current cell isnot acquired as the UE is powered on or newly moves to the current cell.If the temporary ID pool is acquired, it means that the UE detectstemporary IDs available in the current cell.

In step 1115, the UE selects one temporary ID from the temporary IDpool. In step 1120, the UE sends the IUM with the selected temporary IDto the Node B. In step 1125, the UE waits for the delay duration Twithout monitoring a DL SCCH after sending the IUM. When the delayduration T has elapsed, the UE monitors the SCCH during the valid periodP in step 1130. The UE determines whether a dedicated short IDallocation message with the selected temporary ID is received on theSCCH in step 1135. If the dedicated short ID allocation message with theselected temporary ID is received in the valid period P, the UE proceedsto step 1145. Otherwise, the UE proceeds to step 1150.

In step 1145, the UE sets a short ID included in the dedicated short IDallocation message to its own dedicated short ID and then transmits andreceives data on the SCH using the dedicated short ID. On the otherhand, the UE determines that the initiation for communications on theSCH has failed and then performs a required subsequent operation in step1150. For example, the UE retransmits the RIM.

FIG. 12 is a block diagram illustrating a structure of the UE inaccordance with an exemplary embodiment of the present invention.

As illustrated in FIG. 12, the UE is provided with a control messagegenerator 1205, a control message processor 1225, a controller 1235, ashort ID manager 1210, a SCCH processor 1215, a SCH processor 1220, adedicated short ID allocation message processor 1240, and a transceiver1230.

Referring to FIG. 12, the controller 1235 controls an operation of theUE related to radio resources. For example, the controller 1235 performsan operation for establishing or releasing a radio channel or anoperation for setting information to be inserted into an uplink controlmessage. The controller 1235 delivers the information to be insertedinto an IUM to the control message generator 1205. For example, thecontroller 1235 manages a temporary ID pool and T and P values acquiredfrom system information of a current cell, selects a temporary ID fromthe temporary ID pool, and delivers the selected temporary ID to thecontrol message generator 1205.

The control message generator 1205 generates the uplink control messageusing the information received from the controller 1235. In particular,the control message generator 1205 generates the IUM using informationsuch as the temporary ID and the like delivered from the controller 1235and delivers the generated IUM to the transceiver 1230. The transceiver1230 transmits a message or data to and receives a message or data froma UE through a radio channel.

When the controller 1235 is notified that the IUM has been transmittedfrom the control message generator 1205, the controller 1235 waits forthe delay duration T and delivers the selected temporary ID and the Pvalue to the dedicated short ID allocation message processor 1240. Thecontroller 1235 controls the dedicated short ID allocation messageprocessor 1240 to monitor messages received on the SCCH during the validperiod P. The SCCH processor 1215 detects a dedicated short IDallocation message among messages of the SCCH received from thetransceiver 1230 and then delivers the detected dedicated short IDallocation message to the dedicated short ID allocation messageprocessor 1240.

The dedicated short ID allocation message processor 1240 compares atemporary ID contained in the dedicated short ID allocation messagereceived from the SCCH processor 1215 with the temporary ID receivedfrom the controller 1235. If the two temporary IDs are same as eachother, the dedicated short ID allocation message processor 1240 deliversa dedicated short ID to the short ID manager 1210.

The short ID manager 1210 activates the short ID received from thededicated short ID allocation message processor 1240. Then, the SCCHprocessor 1215 detects per packet control information contained in amessage with the activated short ID among messages received on the SCCHand then delivers the detected per packet control information to the SCHprocessor 1220. When receiving the per packet control information fromthe SCCH processor 1215, the SCH processor 1220 detects a packet fromthe SCH, processes (or demodulates/decodes) the detected packet usingthe per packet control information, and delivers a successfullyprocessed packet to a suitable device. When the packet includes an IDMtransmitted on the SCH, the IDM is delivered to the control messageprocessor 1225. Otherwise, the packet is delivered to an associatedapplication section.

The control message processor 1225 delivers control informationcontained in the IDM to the controller 1235. The controller 1235provides the short ID manager 1210 with a dedicated short ID of theinformation delivered from the control message processor 1225. At thistime, an activation period of the dedicated short ID is continuouslymaintained until a special command is issued. The short ID manager 1210controls the SCCH processor 1215 to detect per packet controlinformation with the dedicated short ID during the activation period ofthe dedicated short ID. Thus, the dedicated short ID is applied fortransmission and reception of data on the SCH.

As is apparent from the above description, the exemplary embodiments ofpresent invention can reduce initiation delay and complexity of a systemand a UE by efficiently initiating communications in a mobilecommunication system for transmitting data and messages on a SCH.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for initiating communications in a userequipment (UE), the method comprising: receiving system informationtransmitted from a base station on a broadcast channel, the systeminformation indicating a group of identifiers for requestingcommunications; selecting a first identifier from among the group ofidentifiers for requesting communications; transmitting an uplink signalcorresponding to the selected first identifier for requestingcommunications to the base station; determine whether a downlink signalresponding to the uplink signal is received on the downlink channel fromthe base station during a predetermined time period, the time periodbeginning at a time point determined based on a value signaled by thebase station, after the transmitting of the uplink signal, the downlinksignal comprising an identifier corresponding to the transmitted uplinksignal; and communicating data with the base station, in response to thedownlink signal being received during the time period.
 2. The method ofclaim 1, wherein the downlink signal further comprises an UE-ID of theUE.
 3. The method of claim 1, wherein the downlink signal furthercomprises one a plurality of IDs in an ID pool of a current cell.
 4. Auser equipment (UE) for performing random access, the UE comprising: areceiver configured to receive system information transmitted from abase station on a broadcast channel, the system information indicating agroup of identifiers (IDs) for requesting communications; a controllerconfigured to: select a first identifier from among the group ofidentifiers, and generate an uplink signal corresponding to the selectedfirst identifier for requesting communications; uplink signal, anddetermine whether a downlink signal responding to the uplink signal isreceived on the downlink channel from the base station during apredetermined time period, the time period beginning at a time pointdetermined based on a value signaled by the base station, after thetransmitting of the uplink signal, the downlink signal comprising anidentifier corresponding to the transmitted uplink signal; and atransmitter configured to: transmit the generated uplink signal to thebase station, and communicate data with the base station, in response tothe downlink signal being received during the time period.
 5. The UE ofclaim 4, wherein the downlink signal further comprises an UE-ID of theUE.
 6. The UE of claim 4, wherein the downlink signal further comprisesone a plurality of IDs in an ID pool of a current cell.
 7. A method forinitiating communications in a base station, the method comprising:transmitting system information on a broadcast channel, the systeminformation indicating a group of identifiers for requestingcommunications; receiving an uplink signal corresponding to a firstidentifier selected from among the group of identifiers for requestingcommunications from a user equipment (UE); transmitting a downlinksignal responding to the uplink signal on a downlink channel within apredetermined time period, the downlink signal comprising an identifiercorresponding to the received uplink signal, the time period beginningat a time point determined based on a value signaled by the basestation, after the transmitting of the uplink signal; and communicatingdata with the UE, in response to the downlink signal being received tothe UE within the time period.
 8. The method of claim 7, wherein thedownlink signal further comprises an UE-ID of the UE.
 9. The method ofclaim 7, wherein the downlink signal further comprises one a pluralityof IDs in an ID pool of a current cell.
 10. A base station forinitiating communications, the base station comprising: a transceiverconfigured to: transmit system information on a broadcast channel, thesystem information indicating a group of identifiers for requestingcommunications, receive an uplink signal corresponding to a firstidentifier selected from among the group of identifiers for requestingcommunications from a user equipment (UE), transmit a downlink signalresponding to the uplink signal on a downlink channel within apredetermined time period, the downlink signal comprising an identifiercorresponding to the received uplink signal, the time period beginningat a time point determined based on a value signaled by the basestation, after the transmitting of the uplink signal, and communicatingdata with the UE, in response to the downlink signal being received tothe UE during the time period; and a controller configured to controlthe transceiver to transmit the downlink signal in the time period. 11.The base station of claim 10, wherein the downlink signal furthercomprises an UE-ID of the UE.
 12. The base station of claim 10, whereinthe downlink signal further comprises one a plurality of IDs in an IDpool of a current cell.